1. Field of the Invention
Embodiments of the invention relate to image sensors. More particularly, embodiments of the invention relate to image sensors having improved photoelectric conversion efficiency and related methods of fabrication.
This application claims priority to Korean Patent Application 2005-08150 filed on Jan. 28, 2005, the subject matter of which is hereby incorporated by reference in its entirety.
2. Discussion of Related Art
Image sensors are electronic devices adapted to transform optical signals definng a visual image into electric signals. Image sensors are widely used in contemporary mobile devices, such as cell phones, digital video and still cameras, personal digital assistants (PDAs), toys, game systems, robots, Personal Computers (PCs), PC cameras, optical mouse devices, scanners, security cameras, infrared cameras, cameras for organism identification and wireless inspection, etc.
In general, the conventional image sensor comprises a light receiver portion adapted to generate electrical charge in response to incident light of defined wavelength, and an electronics portion adapted to process the generated electrical charge received from the light receiver portion. The performance quality of any given image sensor may be evaluated according to such characteristics as sensitivity, responsivity, dynamic range, uniformity, shuttering, speed, and noise.
In order to improve the performance characteristics of an image sensor, it is necessary to address the issue photoelectric conversion efficiency, or the efficiency with which the image sensor converts incident light signals to corresponding electrical signals. Since the overall photoelectric conversion efficiency of an image sensor is the product of several variables, including quantum efficiency, condensing rates of related microscopic lenses, etc., many different approaches have been taken to the improvement of photoelectric conversion efficiency. In this regard, the quantum efficiency component contributing to the overall efficiency of photoelectric conversion may deteriorate due to such effects as the: (1) reflection differences caused by various refractive indexes for films disposed along a path for the incident light; (2) diffraction at the openings of photodiodes; and (3) transmission of photodiodes.
It should further be noted that photoelectric conversion efficiency is often a product (i.e., varies with) the incident light wavelength. For example, the penetration depth of incident light into the surface of active elements forming the conventional image sensor increases with wavelength. Thus, incident light in the red range (e.g., incident light having a wavelength of about 700 nm) may penetrate up to three times (3×) deeper into a conventional photodiode structure than incident light in the blue range having a much shorter wavelength.
The resulting variance as a function of incident light wavelength presents a real challenge to the problem of providing an image sensor having a desired, flat photoelectric conversion efficiency. Many conventional image sensors have problems with low composition of red color and asymmetrical color ratios. Moreover, the electron-hole pairs generated by the red color incident light penetrating to a relatively greater depth within the photodiode, may flow into the photodiode regions of adjacent pixels, thereby inducing the problem of crosstalk (i.e., inter-pixel noise).